Is this some "I didn't kill you, I just tied you up and left you on the tracks at 11:55 for the noon train" distinction?
And just because the attacks aren't explicitly coordinated on the site doesn't mean there's not culpability there... if an 8chan user is radicalized by 8chan and attacks a target suggested by 8chan, that doesn't mean 8chan isn't responsible just because the user didn't explicitly type "yes I am going to attack on Febtober 7th at 2pm".
That's sort of the problem with the whole "stochastic terrorism" thing... there's a transparently thin veneer of deniability for everyone involved, even the leaders. We obviously don't tolerate those excuses when dealing with jihad, you're going to get sanctioned or even bombed even if you're "just their spiritual leader and not actually involved with planning.
There's no reason to with 8chan or KF either.
Both of those things are EXPLICITLY against the rules and are heavily enforced. They only take public information and are point and laugh, but don't touch.
Reprehensible for sure, but your portrayal isn't accurate.